The present invention relates generally to operations performed in conjunction with subterranean wells and, in an embodiment described herein, more particularly provides a well control system utilizing a subsurface electro-hydraulic power unit.
It is common practice to control operation of a downhole hydraulically actuated well tool, such as a safety valve, from the earth's surface using fluid pressure transmitted from the surface to the tool via hydraulic lines, or control lines. Where the tool is within a few thousand feet of the surface, this method is quite satisfactory in practice. However, where the tool is located more than a few thousand feet deep in the well, hydrostatic pressure in the control lines, resistance to fluid flow through the control lines, the cost of running the control lines, the danger of damage to the control lines, the increased number of control line couplings and, therefore, potential leak paths, and other factors make this method unfeasible, or at least undesirable.
To solve this problem, hydraulically actuated well tools may be discarded in favor of electrically actuated well tools, or the hydraulically actuated well tools may be redesigned so that some other means is used to actuate the tools. Unfortunately, this solution to the problem requires that substantial costs be incurred in making changes to existing well tools having proven capabilities and reliable operation histories, etc.
Therefore, it may be readily seen that it would be quite desirable to provide a method whereby existing hydraulically actuated well tools may be remotely operated from the surface, without requiring use of hydraulic control lines extending between the surface and the tools.